It is known that the control unit of an orthopedic foot part, in the form of an artificial foot or foot orthotics, should satisfy a number of requirements to enable a safe use of the foot and enable the prosthesis wearer to have a motion sequence which is as natural as possible when walking. For example, during walking it is desirable for the foot part to allow a controlled impact on the standing plane when the heel impacts, and to allow a controlled heel-toe motion over the forefoot during which the body of the prosthesis wearer is slightly lifted. The natural foot undergoes dorsiflexion during the swing phase, resulting in a shortening of the leg-length, and hence an eased swing-through. Furthermore, safe standing on the artificial foot requires a high rigidity of the angle between the foot part and the connection part for the lower leg. However, in this case expedient blocking of the swivel joint of the artificial foot, which swivel joint acts as the ankle joint, should be adjustable so that the prosthesis wearer can stand on inclined ground or in a shoe with a relatively high heel in a relaxed manner.
For example, US 2005/0197717 A1 discloses controlling the ankle angle during a gait cycle by means of an actuator in the form of a double-screw motor. In the process, a foot part is used which is intended to contribute to implementing an approximately natural gait by having a defined elasticity. Using an actuator in the form of a continuously driven motor requires a large amount of electrical energy which has to be supplied to the artificial joint. To this end, the prosthesis wearer must carry a powerful battery which must have a large volume and be heavy due to the required large capacity.
Furthermore, only controlling a damping of the rotational movement of the foot part relative to the connection part is known in order to satisfy some aspects of the control. To this end, U.S. Pat. No. 7,029,500 B2 discloses a special swivel joint as an ankle joint of the artificial foot, with the damping being influenced by a magneto-rheological liquid by virtue of the fact that applying a magnetic field makes it possible to switch the viscosity of the fluid from low to high, and hence the damping can be switched from low to high. This makes it possible to lock a dorsiflexion or plantar flexion which is automatically set during walking, and maintain it for a certain amount of time. This also makes it possible for the joint to be released when seated in order to set a plantar flexion setting which is also effected by the natural foot when seated.
Furthermore, US 2002/0138153 A1 discloses the use of a hydraulic arrangement for setting the rest angle when standing on inclined ground or for the different heel heights of a shoe used with the artificial foot, in which hydraulic arrangement the liquid flows from one liquid reservoir to the other in the case of a plantar flexion, and in the opposite direction for a dorsiflexion. An electromagnetic coil is inserted in a connecting line between the two liquid reservoirs and it controls the viscosity of the magneto-rheological liquid used as the hydraulic liquid; as a result of this, the damping can be switched between a first damping level and a second damping level. In order to satisfy the demanded control objectives, an inclination sensor for the lower leg part with respect to the perpendicular and a floor contact sensor are used. The floor contact sensor indicates that the artificial foot is experiencing a floor reaction force as a result of stepping on the floor.